Integrated interface architecture and control logic for enhanced emergency location functionality

ABSTRACT

Aircraft tracking and emergency location avionics architectures that integrate existing fixed Emergency Locator Transmitter (ELT) installations, their associated aircraft avionics systems and existing flight deck interfaces with an Autonomous Distress Tracker (ADT) transceiver unit in a coupled configuration. Some of the architectures allow the ADT unit and its advanced distress detecting and reporting capabilities to monitor the activation control path for the ELT and the associated ELT activation outputs. Other architectures place the ADT unit and its advanced distress detection capabilities and ground-controlled capabilities in the activation control path for the ELT. Additional architectures entail the connection of an ADT unit to an ELT remote panel on the flight deck of an aircraft.

BACKGROUND

The technology disclosed herein generally relates to systems and methodsfor detecting and locating an aircraft in distress. More particularly,the technology disclosed herein relates to integrated aircraft distresssystem architectures capable of providing emergency locationfunctionality.

Most commercial airliners are equipped with fixed Emergency LocatorTransmitters (ELTs) that broadcast beacons and satellite uplinks in thecase of an emergency to enable search and rescue crews to find theaircraft. In some recent aircraft emergencies, however, the ELTs werenot activated. Such incidents have shown the importance of providing amore reliable and tamperproof method to provide an accurate and timelyaircraft location tracking, including the highly accurate tracking of anaircraft in a distress condition. Autonomous Distress Trackers (ADTs)are an emerging class of aircraft systems that support this need.

Based on the current methods of installing normal (non-distress,non-tamper-proof) tracking systems, ADTs for aircraft will typically beinstalled as stand-alone installations, e.g., there is the existingfixed ELT installation and a separate stand-alone ADT installationinstalled by itself or in addition to the existing ELT installation.

These separate installation approaches have a number of drawbacks;including new flight deck hardware to support the crew interfaces to theADT, no improvements to the current ELT performance limitations, and twouncoupled emergency systems that require separate crew actions andpotentially unsynchronized activation that may result in less effectiveemergency notifications and ambiguous signals to the emergencyresponders. Integrating these installations is a significant challengedue to the wide range of existing ELT manufacturers and interfaces andthe range of flight deck and avionics interfaces potentially involved.

The foregoing shortcomings can be addressed by providing a system and amethod that maximizes emergency or aircraft-in-distress locationcapabilities. To facilitate early and wide adoption, theaircraft-in-distress location tracking system should be designed tofacilitate simplified and low-cost aircraft integration andinstallation.

SUMMARY

The subject matter disclosed in detail below includes multipleintegrated ADT-ELT architecture configurations that address one or moreof the above-described shortcomings—by reusing existing crew interfacesto reduce installation costs, crew training and crew workload in anemergency, by providing multiple options to synchronize the emergencybroadcasts by ADT and ELTs, and by providing an option to significantlyimprove existing fixed ELT emergency performance and hence the emergencyperformance of the overall system. These integrated ADT-ELT architectureconfiguration options are enabled by an innovative common ADT interfacearchitecture that supports a wide range of existing ELT and flight deckinterfaces and multiple means of integrating ADT and ELTs depending onthe degree of coupling desired by an airline or allowed by regulatoryauthorities. (As used herein, the term “common” means belonging to orshared by two or more components, not occurring or appearingfrequently.)

More specifically, the aircraft tracking and emergency location avionicsarchitectures disclosed herein integrate existing fixed ELTinstallations, their associated aircraft avionics systems and existingflight deck interfaces with an ADT unit in a coupled configuration. Someof the architectures allow the ADT unit and its advanced distressdetecting and reporting capabilities to monitor the activation controlpath for the ELT and the associated ELT activation outputs (referred toherein as “loosely coupled configurations”). Other architectures placethe ADT unit and its advanced distress detection capabilities andground-controlled capabilities in the activation control path for theELT (referred to herein as “medium coupled” or “tightly coupled”configurations). Additional architectures entail the connection of astand-alone ADT unit to an ELT remote panel on the flight deck of anaircraft and/or an “ELT ON” discrete input in the aircraft avionics.

The loosely coupled (or “parallel”), medium coupled (or “enhancedparallel”) and tightly coupled (or “series”) integrated ADT-ELTconfigurations provide multiple improvements over non-integratedconfigurations, including reusing existing crew interfaces to reduceinstallation costs, crew training and crew workload in an emergency, andproviding for the synchronization of emergency broadcasts by ADT andELTs. The loosely coupled configuration further provides enhancedaircraft state awareness to the ADT and associated ground systems andhence improves the emergency performance of the overall system. Themedium and tightly coupled configurations significantly improve existingfixed ELT emergency performance and hence the emergency performance ofthe overall system. This significant performance improvement is achievedby allowing the ADT to trigger ELT distress broadcasts, using, forexample, ADT internal trigger conditions indicating aircraft non-normalor distress flight conditions or ground segment commands uplinked froman airline operation center. The medium and tightly coupledconfigurations may also support improved emergency reporting in thepresence of SATCOM network congestion or RF interference scenarios. Thetightly coupled configuration provides the opportunity to filter flightcrew inputs to the ELT, resulting in potentially reduced false alarms.The medium coupling configuration does not support the filteringfunction, but may provide a more straightforward certification.

The above-described configuration options are enabled by unique ADTarchitecture features that support multiple means of interfacing the ADTto a broad range of existing fixed ELTs and their aircraft interfaces.This ADT interface architecture supports these multiple integration andinstallation options, including a minimum impact “parallel” ADT-ELTinstallation option, “series” and “enhanced parallel” ADT-ELTinstallation approaches that significantly enhance the capabilities ofthe existing ELTs, and potentially a “stand-alone” ADT installation thatallows the deletion of the fixed ELTs currently installed on manyaircrafts with minimal impacts on the existing aircraft systeminterfaces and aircraft operations.

The above-described configuration options may provide significantadvantages for emergency location and aircraft distress trackingperformance combined with lower installation, integration and trainingcosts compared to some non-integrated or stand-alone architectures.

One aspect of the subject matter disclosed in detail below is an ADTunit comprising: first processing means comprising ELT activation logic;and an input interface comprising first, second and third terminals andsecond processing means configured to output an ELT ON state signal tothe ELT activation logic if an impedance between the first and thirdterminals is effectively zero or if an impedance between the first andsecond terminals is effectively zero. In accordance with someembodiments, the first and second processing means comprise a commonprocessor. In accordance with some embodiments, the first processingmeans comprise a first processor and the second processing meanscomprises a second processor. The input interface may further comprise ahigh-impedance buffer circuit connected to the first, second and thirdterminals, and an analog-to-digital converter disposed between thehigh-impedance buffer circuit and the second processing means.

In some embodiments of the ADT unit described in the precedingparagraph, the first processing means further comprises an aircraftbehavior state estimator and ADT trigger logic that receives anestimated aircraft behavior state signal from the aircraft behaviorstate estimator and the ELT ON state signal from the second processingmeans, and is configured to send an ELT activation request signal to theELT activation logic if the estimated aircraft behavior state signalindicates an abnormal or distress state or an ELT ON state signal hasbeen received.

Another aspect of the subject matter disclosed in detail below is asystem onboard an aircraft comprising: an ELT remote panel on the flightdeck of the aircraft, the ELT remote panel comprising a switch; a firstantenna that is attached to an exterior of a fuselage skin of theaircraft; and an ADT unit connected to the first antenna and comprising:first processing means comprising ELT activation logic; and a firstinput interface comprising first, second and third terminals, and secondprocessing means configured to output an ELT ON state signal to the ELTactivation logic if an impedance between the first and third terminalsis effectively zero or if an impedance between the first and secondterminals is effectively zero, wherein the switch of the ELT remotepanel is connected to the first terminal of the first input interface bywiring. When the ELT remote panel switch has a first switchconfiguration, the switch is not connected to either of the second andthird terminals of the first input interface and the third terminal ofthe first input interface is connected to ground. When the ELT remotepanel switch has a second switch configuration different than the firstswitch configuration, the switch is also connected to the secondterminal of the first input interface by wiring and the third terminalof the first input interface is connected to ground.

The system described in the preceding paragraph may further comprise: asecond antenna that is attached to an exterior of a fuselage skin of theaircraft; and an ELT unit connected to the second antenna and to the ADTunit, in which case the ELT unit can also be connected to the switch ofthe ELT remote panel.

The ADT unit may further comprise a first output interface thatcomprises a terminal connected to the ELT unit and third processingmeans configured to output an ELT ON state signal to the terminal of thefirst output interface in response to receipt of an ELT ON state signalfrom the ELT activation logic. In some embodiments, the ELT activationlogic comprises trigger activation filtering logic and triggeractivation input pass-through logic configured to apply the ELT ON statesignal to the terminal of the first output interface subject to thetrigger activation filtering logic.

In accordance with some embodiments of the above-described system, thefirst processing means further comprises an aircraft behavior stateestimator and trigger logic that receives an estimated aircraft behaviorstate signal from the aircraft behavior state estimator and the ELT ONstate signal from the second processing means, the trigger logic beingconfigured to send an ELT activation request signal to the ELTactivation logic if the estimated aircraft behavior state signalindicates an abnormal or distress state or an ELT ON state signal hasbeen received. In this case, the ELT activation logic comprises crewactivation filtering logic and crew activation input pass-through logicconfigured to apply the ELT ON state signal from the second processingmeans to the terminal of the first output interface subject to the crewactivation filtering logic.

The system may further comprise an aircraft avionics system, wherein theADT unit further comprises a second input interface and a second outputinterface connected to the aircraft avionics system by wiring.

A further aspect of the subject matter disclosed in detail below is amethod for equipping first and second aircraft with first and second ADTunits of identical design having first, second and third terminals,wherein the first aircraft has a flight deck equipped with a first ELTremote panel switch having a first switch configuration and the secondaircraft has a flight deck equipped with a second ELT remote panelswitch having a second switch configuration different than the firstswitch configuration, the method comprising: connecting the first andsecond terminals of the first ADT unit to the first ELT remote panelswitch by wiring; connecting the first terminal of the second ADT unitto the second ELT remote panel switch by wiring; and connecting thethird terminal of the second ADT unit to ground. This method may furthercomprise: connecting a fourth terminal of the first ADT unit by wiringto a first ELT unit onboard the first aircraft; and connecting a fourthterminal of the second ADT unit by wiring to a second ELT unit onboardthe second aircraft.

Other aspects of systems and methods for location tracking of aircraftin distress are disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, functions and advantages discussed in the precedingsection can be achieved independently in various embodiments or may becombined in yet other embodiments. Various embodiments will behereinafter described with reference to drawings for the purpose ofillustrating the above-described and other aspects.

FIG. 1 is a diagram showing a typical stand-alone ELT architecture.

FIG. 2 is a block diagram identifying some major components andinterfaces of a typical ELT.

FIG. 3 is a block diagram identifying major subsystems of a globalaircraft tracking system having an ADT unit as part of an airbornesegment in accordance with some embodiments.

FIG. 4 is a diagram showing major components of an ADT airborne segment(including an ADT unit) for a stand-alone ADT architecture.

FIG. 5 is a block diagram identifying some components and interfaces ofan ADT unit in accordance with one embodiment.

FIG. 6 is a diagram showing an architecture in which ELT and ADTs areseparate and not coupled to each other.

FIG. 7 is a diagram showing a stand-alone ADT architecture with re-useof an ELT flight deck control panel configuration in accordance with afirst embodiment.

FIG. 8 is a diagram showing a non-coupled ADT-ELT architecture withcommon use of an ELT flight deck control panel configuration inaccordance with a second embodiment.

FIG. 9 is a diagram showing an architecture in which an existing fixedELT installation has been replaced by an ADT system in accordance with athird embodiment featuring re-use of an ELT flight deck control paneland ELT inputs to an aircraft avionics systems.

FIG. 10 is a diagram showing a loosely coupled (i.e., in parallel)ADT-ELT integrated architecture configuration in accordance with afourth embodiment.

FIG. 11 is a diagram showing a tightly coupled (i.e., in series) ADT-ELTintegrated architecture configuration in accordance with a fifthembodiment.

FIG. 12 is a diagram showing an ADT-ELT integrated architectureconfiguration with medium coupling (i.e., enhanced parallel) inaccordance with a sixth embodiment.

FIG. 13 identifies inputs to and outputs from a common ADT unit that canbe incorporated in any one of the configurations depicted in FIGS. 4 and6-12.

FIG. 14 is a diagram identifying ADT major functions and interfaces.

FIG. 15 is a diagram depicting functions that an ADT common aircraftdiscrete input interface should include to support a broad range ofaircraft avionics integration options.

FIG. 16 is a diagram depicting functions that an ADT common aircraftdiscrete output interface should include in order to support a broadrange of aircraft avionics integration options.

FIGS. 17A and 17B are diagrams depicting the internal wiring of theflight deck panel switch in accordance with respective ELT remote panelswitch configurations.

FIG. 17C is a diagram depicting a common ELT crew activation inputinterface function that allows ADT integration with either of the switchconfigurations shown in FIGS. 17A and 17B.

FIG. 18 is a diagram depicting functions that a common ELT activationinput interface function that allows ADT integration with a broad rangeof ELT units.

FIGS. 19A and 19B are diagrams showing respective ELT activation outputconfigurations that support various possible ELT configurations.

FIG. 19C is a diagram depicting a common ELT activation output interfacefunction that allows ADT integration with ELT units having either of theactivation configurations shown in FIGS. 19A and 19B.

FIG. 20 is a block diagram showing some hardware components of the ADTunit, including interface circuitry and a microprocessor that executesone or more of the interface sensor functions identified in FIGS. 17C,18 and 19C.

FIG. 21 is a diagram identifying components of the ADT trigger logic andaircraft behavior state estimator in accordance with one embodiment ofthe ADT unit.

FIG. 22 is a block diagram identifying components of an ELT activationlogic function for an ADT unit.

FIGS. 23A through 23D are diagrams showing different switchconfigurations for outputting discretes: a 28-V discrete (FIG. 23A); a5-V discrete (FIG. 23B); an Open/Ground discrete (FIG. 23C); and anOpen/Closed discrete (FIG. 23D).

In FIGS. 1, 4 and 6-12, the following symbology has been adopted: anyline connecting two components and having no arrowhead representsaircraft wiring for carrying RF electrical signals (e.g., RF coaxialcable); any line connecting two components and having at least onearrowhead represents aircraft wiring for power or data; any dashed arrowrepresents an RF signal path; and any zigzag-shaped arrow represents RFsignals propagating through the atmosphere.

Reference will hereinafter be made to the drawings in which similarelements in different drawings bear the same reference numerals.

DETAILED DESCRIPTION

Illustrative embodiments of an aircraft-in-distress location trackingsystem are described in some detail below. However, not all features ofan actual implementation are described in this specification. A personskilled in the art will appreciate that in the development of any suchactual embodiment, numerous implementation-specific decisions must bemade to achieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which will vary fromone implementation to another. Moreover, it will be appreciated thatsuch a development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking for those of ordinary skill in theart having the benefit of this disclosure.

The embodiments disclosed below utilize existing aircraft informationsystems and existing aircraft power systems. These existing aircraftsystems will vary in their specifics depending on the aircraft model andavionics architectures used. For the purposes of the current disclosure,virtually all will support the interfaces described, although thespecific location/sourcing unit may vary.

The existing fixed ELT system (that is being replaced or integratedwithin the configurations disclosed below) comprises an ELT, of whichthere are multiple variations from multiple manufacturers. Theinterfaces described in this disclosure are common across those used bymany (probably most or all) commercial airliners. The existing fixed ELTsystem further comprises an externally mounted ELT antenna and a flightdeck-mounted ELT switch. This switch can vary by aircraft and ELT model.The interface architecture described herein enables the variousintegrated or stand-alone architectures by supporting the ELT switchinterfaces for many (probably most or all) commercial airliners andELTs.

The ADT system components depicted in the drawings comprise an ADT unit,which hosts most of the ADT system functionality, and an externallymounted ADT antenna. Another potential ADT system component is anADT-specific flight deck control panel. The architectures disclosedbelow support this option, but they also support re-use or shared use ofthe existing ELT flight deck switches to reduce installation costs,enhance operational awareness and reduce training and documentationcosts.

The ELTs as currently implemented on aircraft have many importantfeatures, including direct crew activation panels, aircraftidentification information for transmissions, locator beacons thatrescue aircraft or ground rescuers can use to locate a crash site, andthe ability to uplink satellite transmissions to the internationalworldwide coverage COSPAS/SARSAT. COSPAS/SARSAT is a search and rescuesatellite system that allows location of persons in distress by means ofthe signals received via the space elements (including the inclusion ofaircraft location in the satellite uplink for newer systems). The systemserves a wide variety of users including those on ships, aircraft andtravelers in remote regions.

ELTs are fairly broadly used within the airline industry with somemodels of wide-body aircraft approaching 100% equipage with ELTs. Thereare many models and manufacturers of ELTs, all built to common standardsbut with varying flight deck interfaces and concepts of operations. Atypical stand-alone ELT installation is shown in FIG. 1. Thisinstallation comprises a fixed ELT unit 30, an ELT antenna 24 mounted onan external surface of a fuselage skin 26, and an ELT remote panel 22 onthe flight deck, which remote panel comprises the aforementioned ELTswitch which can be manually operated by a member of the flight crew.The main transmitter control switch is labeled “ON”—“ARM”. The switch isin the armed position for normal operations. The ELT remote panel 22also has input means for sending ELT test/reset inputs to the ELT unit30 and means for annunciating the state of the ELT unit 30 in responseto crew annunciation outputs received from the ELT unit 30. The ELT unit30 can be triggered by ELT activation inputs 64 from the ELT remotepanel 22 and/or activation inputs from sensors (not shown in FIG. 1, butsee FIG. 2) internal to the ELT unit 30 that detect the impact forceproduced during a crash. In response to a trigger event, the ELT unit 30outputs electrical signals to the ELT antenna 24, which cause the latterto broadcast a 406-MHz rescue beacon to the COSPAS/SARSAT rescuesatellite system. The rescue beacon transmits bursts of digitalinformation to orbiting satellites, and also contains a small integratedanalog (121.5/243 MHz) homing beacon. Advanced beacons encode a GPS orGLONASS position into the signal. The fixed ELT unit 30 also sends anELT activation output 68 (indicating that the ELT unit 30 has beenactivated) to the aircraft avionics systems 28.

FIG. 2 identifies some components of a typical ELT unit 30. In theembodiment depicted in FIG. 2, the internal sensors 46 includeG-switches that detect high accelerations/decelerations indicative of acrash impact for multiple axes and high-temperature switches that detecttemperatures associated with a fire. The states of the internal switches46 are stored in a latching circuit 48, which is powered by a batterypack 50. All functions of the ELT unit 30 are under the control of amicroprocessor 52, which receives electrical power from the battery pack50 via the latching circuit 48. In the event of a crash, themicroprocessor 52 activates the transmitter 54 to transmit the standardswept tone on 121.5 MHz, lasting until battery power is exhausted. This121.5-MHz signal is mainly used to pinpoint the beacon during search andrescue operations. In addition, for the first 24 hours of operation, themicroprocessor periodically activates the transmitter 56 to transmit a406-MHz signal, e.g., at 50-second intervals. This transmission containsidentification data programmed into the beacon, which is received by theCOSPAS-SARSAT satellites. The transmitted data is referenced in adatabase (maintained by the national authority responsible for ELTregistration) and used to identify the beacon and owner.

The ELT activation methods have a number of significant issues, theprimary one of which is a limited success rate in locating majorcrashes. These limitations arise primarily due to the activationmethods, i.e., the internal sensors activate upon a crash event withsufficient decelerations/accelerations. The issues from this primary ELTconcept of operations include:

1) Crash impacts that do not have sufficient decelerations to triggerthe ELT. These may occur because of lower speeds, impact attitudes etc.

2) Failure of the flight crew to activate the ELT. This may be due tothe flight crew being fully engaged with aircraft recovery attempts orit may be due to flight crew members intentionally not activatinglocation equipment.

3) Crash impacts that take place with aircraft attitudes that interferewith transmissions. For example, an aircraft that impacts while invertedwould place the ELT system in a position where its transmissions couldnot be uplinked).

4) Crash impacts which disable the ELT system (e.g., shearing off theELT antenna before the location can be uplinked or determined) or whichblock ELT transmissions (e.g., where the antenna is immersed in water).

5) A final concept of operations-based limitation is that ELTs must relyon large internal batteries for power since the crash forces that mayactivate them may also disable aircraft power sources. These internalbatteries can be a source of issues as well and there is significantinterest in reducing or doing away with these batteries.

The standards for a second generation of ELTs are in process. Therequirements in this developing standard address the aforementionedissue of limited success rate in crash location by focusing on fusingextensive internal aircraft state information, such as the status of theaircraft engines, with aircraft trajectory and attitude information toprovide new, high-assurance trigger inputs to the second-generation ELTsto activate the emergency transmissions upon indications that a crash isprobable.

This second-generation ELT approach has a number of drawbacks forimplementation, including requiring fairly extensive use of a diverseset of aircraft avionics data inputs and trigger algorithmimplementation in already highly integrated and tightly regulatedavionics components. These implementation issues, while intended tosupport addressing the technical issues with current ELTs, will imposesignificant operational costs. In particular they will require extensivedevelopment and certification time and costs that will need to bereplicated for multiple aircraft/avionics architectures and they willhave significant installation costs that will probably result insignificant impacts on airline uptake and uptake timing for implementingthese capabilities in their operational aircraft.

ADT systems are another rapidly emerging class of systems. ADT systemssupport aircraft emergency location as well as normal aircraft tracking.These systems generally include airborne-based components (the airbornesegment), space-based communications and positioning functions (thespace segment) and ground-based control and reporting functions (theground segment).

FIG. 3 identifies major subsystems of a global aircraft tracking systemhaving an ADT airborne segment 12 in accordance with some embodiments.The ADT airborne segment 12 is installed on an aircraft platform 10(e.g., a commercial aircraft). The global aircraft tracking system alsoincludes a space segment and a ground segment. The space segmentconsists of the commercial SATCOM constellation 2 and the GNSSconstellation(s) 4. The ADT airborne segment 12 communicates with thesatellites of the SATCOM constellation 2 via a two-way data packet-basedRF communication link 14 and receives Global Navigation SatelliteSystems (GNSS)-based positioning data 16 from the satellites of the GNSSconstellation(s) 4. A ground station 6 communicates with the satellitesof the SATCOM constellation 2 via a two-way data packet-based orcircuit/connection based RF communication link 18 and communicates withan ADT ground segment 8 via a terrestrial data network 20. The ADTground segment 8 provides the aircraft-in-distress location trackingservice disclosed herein. In particular, the ADT ground segment 8monitors and controls the ADT airborne segment 12 and disseminates datafrom the ADT airborne segment 12. This information can then be sent toother systems and stakeholders such as airline operation centers and airnavigation service providers.

Some ADT units have minimal integration with aircraft avionics systemsand limited crew interfaces. This limited integration significantlysimplifies installation requirements and overall system variation fromaircraft model to aircraft model and airline to airline and associatedcosts of this variation. An ADT system will typically also implementsome degree of tamper-proof design features to limit or do away with theflight crew ability to disable tracking.

In accordance with some configurations, the ADT system may have adedicated specially designed flight deck interface and a generalinterface to aircraft data-buses and general support for aircraft inputand discrete output interfaces. A typical stand-alone ADT configurationfor the airborne segment 12 onboard an aircraft platform is depicted inFIG. 4. This installation comprises an ADT unit 40, an ADT antenna 44mounted on an external surface of a fuselage skin 26, and an ADTactivation control 42 on the flight deck, which can be manually operatedby a member of the flight crew. The ADT unit 40 also receives discreteinputs 70 from the aircraft avionics systems 28. The ADT unit can betriggered to transmit a distress signal based on the crew activationinputs 65 from the ADT activation control 42 and the discrete inputs 70from the aircraft avionics systems 28.

Discrete inputs and outputs are simple and environmentally robust meansof sending signals between avionics units. Discrete data inputs andoutputs use analog signals that are typically limited to two states, theequivalent of ON or OFF. These two states can be implemented by a highvoltage level (typically 5 V or 28 V) versus a grounded (0 V) level oran open circuit (infinite impedance) versus a closed circuit (zeroimpedance). FIGS. 23A through 23D are diagrams showing different switchconfigurations for outputting different types of discretes: a 28-Vdiscrete (FIG. 23A); a 5-V discrete (FIG. 23B); an Open/Ground discrete(FIG. 23C); and an Open/Closed discrete (FIG. 23D). (In FIGS. 23A-23D,“SW” indicates a switch and “R” indicates a resistor.) Using discretesto transmit signals is very limiting in the amount of data that can betransferred. These are typically used to signal the changing ofrelatively infrequent events, for example, an ELT activation. However,these are very robust signaling paths that are largely immune to noiseand do not require closely synchronized system clocks.

In addition, the ADT unit 40 receives the GNSS signals and transmitsrelevant tracking information such as current aircraft latitude,longitude, altitude and attitude to the communication satellites usingthe ADT antenna 44. More specifically, the ADT unit 40 receives radiofrequency (RF) inputs from the ADT antenna 44, including satellitecommunications (SATCOM) RF inputs 58 (e.g., messages from the groundsegment over the Iridium network), GPS RF inputs 60 and GLONASS RFinputs 62. The ADT unit 40 also provides SATCOM RF outputs 74 to the ADTantenna unit 44 (e.g., messages to the ground segment over the Iridiumnetwork).

A typical ADT system will integrate ADT internal rate sensors data andADT-developed GNSS position data with trigger algorithms that evaluatecombinations of aircraft positions, rates and attitudes to determine ifthe aircraft is in distress or abnormal conditions. These capabilitiesare used to support high accuracy, tamperproof aircraft tracking undernormal, abnormal, and distress conditions. The ADT unit 40 also receivesconfiguration commands from the ground to set trigger conditions forincreased report rate for certain regions, during times of distress, orto increase report rate for an aircraft as desired by the operator.

The ADT system provides two related capabilities:

(a) An ability to track an aircraft with a high degree of accuracy innear real-time over worldwide operations during normal aircraftoperating conditions. This normal condition tracking capability isequivalent to that found in existing aircraft tracking systems, but withthe additional characteristic of being autonomous and tamperproof—i.e.,a capability that cannot be disabled by the crew while the aircraft isin flight.

(b) A reliable ability to provide search and rescue organizations withhighly accurate aircraft position data in the event of an aircraft inabnormal conditions or a distress situation. This abnormal/distresstracking and positioning function provides a capability similar to theexisting automatic ELTs, involving transmissions providing aircraftidentification and location information in the event of abnormal ordistress conditions. This capability is provided using an internalsensor and the existing crew activation interfaces to sendhigh-reporting-rate position reports to the ADT ground segment. ExistingELTs use crew activation or internal sensor inputs (G-switches)indicating a potential crash to trigger transmissions on theCOSPAS/SARSAT constellation frequencies and on search and rescue beaconfrequencies. The ADT system is intended to supplement or replaceexisting ELTs by providing superior aircraft location capabilitiesthrough the detection and reporting of aircraft position while theaircraft is in a distress state prior to a crash rather than after acrash has taken place.

The ADT system disclosed herein is also intended to support broadretrofit applicability for aircraft. To facilitate retrofitting, the ADTunit 40 may be in the form of a line replaceable unit (LRU) locatedwithin the fuselage pressure vessel. The ADT unit 40 may be either acrown-mounted unit or a lower lobe rack-mounted unit. For both the crownmount and the lower lobe rack mount options, the ADT unit 40 will betypically installed in the aft fuselage (aft of the wing rear spar andforward of the aft pressure bulkhead). The ADT unit 40 should be mountedon secondary (not primary) aircraft structure.

FIG. 5 is a block diagram identifying some components of an ADT unit 40in accordance with one embodiment. The ADT unit 40 comprises GNSSprotection circuitry 80 connected to the ADT antenna 44, a GPS receiver82 connected to GNSS protection circuitry 80, a SATCOM transceiver 84connected to a SATCOM bandpass filter 98, and an ADT processor 88connected to the GPS receiver 82 and the SATCOM transceiver 84. The ADTprocessor 88 communicates with ADT storage 90 (i.e., a non-transitorytangible computer-readable medium), aircraft control/status interfaces92, and an attitude sensor 94. The ADT unit 40 further comprises a powersupply 86 that supplies electrical power to the ADT processor 88 andaircraft control/status interfaces 92. Optionally, the ADT unit 40 maybe connected by aircraft power input 76 to a rechargeable battery module96. This interface also provides indication of loss of aircraft power ifthe battery module is the direct power source.

As seen in FIG. 5, the aircraft control/status interfaces 92 receivecrew activation inputs 65 from the flight deck and discrete inputs fromthe aircraft avionics systems 28, and may send an ADT ON (distress)output 66 to the aircraft avionics systems 28 when a distressed state isdetected.

The ADT processor 88 is programmed with navigation data functionality(see ADT position and attitude data function 102 in FIG. 14) that takesinput data from the GPS RF inputs, digital aircraft navigation inputs,data from internal sensors and data validity inputs and estimates andcombines these per internal source prioritization logic or an inputground segment source command to provide high-quality estimates ofaircraft location, speeds, track, attitudes and rates for use by otherADT functions and for inclusion in aircraft location/state reports.

There are several limitations for a typical ADT system. These include:

1) Dependence on commercial satellite networks (generally very highcapability and reliability but with possible congestion issues andpossible evolving business impacts on cost and availability).

2) Generally not making use of the COSPAS/SARSAT satellite system andits dedicated worldwide search and rescue links and bandwidth and directsupport for search aircraft capabilities and reports to search andrescue command and control centers.

3) Based on the approach taken by the similar normal tracking systems,ADT flight deck interfaces will typically be dedicated tracking controlinterfaces requiring changes to the flight deck and to flight crewoperations (with attendant training and documentation impacts). Thesechanges will vary from aircraft model and potentially from airline toairline, potentially increasing installation and training costsassociated with these systems.

4) No synchronization with the ELT and associated potentiallydifferent/unsynchronized crew inputs and emergency/distress statereporting.

FIG. 6 is a diagram showing an architecture in which the ELT and ADT areseparate and not coupled to each other. This non-integrated ADT-ELTinstallation addresses several of the limitations of the stand-alonesystem—for example, it uses both the commercial SATCOM networks and theCOSPAS/SARSAT satellite system. Non-integrated installations have otheradvantages, including simplified design requirements and no risk of anyrequirements to revisit ELT installation re-certification due to ELTconfiguration changes. However, other limitations for the stand-alonesystems still apply in this case and other new ones are introduced.

The limitations of the configuration shown in FIG. 6 include:

1) ADT and ELT flight deck interfaces are separate and different,requiring changes to the flight deck and to flight crew operations (withattendant training and documentation impacts). These changes will varyfrom aircraft model to aircraft model and potentially from airline toairline, potentially increasing installation and training costsassociated with these systems. The differences between the interfacesincrease both training costs and potentially crew workload in anemergency situation.

2) No synchronization of the ADT and ELT systems and associatedpotentially different/unsynchronized crew inputs and emergency/distressstate reporting.

3) The ELT limitations previously described in connection with thestand-alone ELT configuration depicted in FIG. 1 are still present.

The ADT-ELT system configurations disclosed hereinafter address thelimitations described above for current ELTs, second generation ELTs andADT systems. The ADT-ELT system configurations disclosed below coverintegration options ranging from non-integrated configurations(described below with reference to FIGS. 8 and 9) with primarily costimprovements to integrated configurations (described below withreference to FIGS. 10-12) which also provide cost improvements togetherwith potentially significant performance improvements over thenon-integrated options.

The non-integrated configurations provide reductions in installationcosts, crew training and crew workload in emergency situations due tothe re-use of crew interfaces and in some cases other aircraftinterfaces. The three basic non-integrated configurations: (1) astand-alone ADT installation for the case where no ELT unit is or hasbeen installed; (2) a separate (non-coupled) ADT-ELT architecture withcommon ELT flight deck control configuration for the case where an ELTunit is installed in addition to an ADT unit and they share the existingELT flight deck switch but are otherwise separate; and (3) an ADTreplacement for ELT configuration where the ADT unit is used to replacean existing ELT unit and the ELT flight switch and associated wiring isreused.

In contrast to the analogous approach shown in FIG. 4, FIG. 7 shows aconfiguration in which the crew interface for the ADT unit 40 can be anexisting ELT remote panel 22. This feature means that no new parts needto be developed for this ADT system's control interface, that existingELT crew interface engineering and installation designs can be used forthe ADT control installation, and that flight crews can use extremelysimilar concepts of operations for ADT activation and ELTactivation—minimizing training and reducing emergency situationworkload.

In contrast to the approach shown in FIG. 6, FIG. 8 shows aconfiguration in which both the ELT unit 30 and the ADT unit 40 areconnected to the ELT remote panel 22. This allows the joint use of thesame ELT switch interface used in the separate ELT installation shown inFIGS. 1 and 7. This provides the advantages of part and installationdesign re-use, as well as the reduced training and emergency workloadcompared to the approach shown in FIG. 6.

FIG. 9 shows an ELT replacement configuration using an ADT unit 40. Thisconfiguration is similar to the stand-alone ADT configuration shown inFIG. 4. The ADT unit 40 receives ELT activation inputs 64 from the ELTremote panel 22 and aircraft discrete inputs 70 from the aircraftavionics systems 28 and transmits an ADT distress output 66 to theaircraft avionics systems 28. In this case, the ADT unit 40 is beingused to replace an existing fixed ELT installation, either in a retrofitto in-service aircraft or as a replacement system during production.This configuration re-uses the existing ELT crew interface andassociated wiring. It also provides an output to the existing ELTactivation input on the existing aircraft avionics using existing wiring(new connectors could be required, but running new aircraft wiring canbe a major impact and expense). This installation option again providesadvantages for part and installation design re-use, as well as actualpart and wiring re-use for both retrofit and forward fit (production)installation. This configuration also provides reduced training andemergency workload compared to the current standard approach.

The above-described non-integrated configurations do not provide anyemergency location performance advantages over the standardnon-integrated configurations. The following paragraphs describe (withreference to FIGS. 10-12) integrated ADT-ELT configuration options thatprovide emergency location performance advantages as well as theinstallation, training and crew workload advantages.

FIG. 10 shows a loosely coupled (i.e., in parallel) ADT-ELT integratedarchitecture configuration which, in addition to reductions ininstallation costs, crew training and crew workload in an emergencysituations, further simplifies installations and crew impacts by the useof a common crew input in the form of the current ELT flight crewinterface and also improves emergency location performance by allowingADT distress outputs from the ADT unit 40 to be triggered by the ELTactivation output 68 from the ELT unit 30 (whether due to crewactivation of the ELT or due to ELT internal activation) as well as thestandard ADT triggers. This also provides a means to alert airlineoperations centers and other ground-based control and monitoring centersof ELT activation in a near real-time manner.

In the configuration shown in FIG. 10, the ADT unit 40 receives flightcrew ELT activation commands 64 output by the existing ELT remote panel22 on the flight deck in parallel to the ELT unit 30, allowing the useof the single existing flight deck control unit with no changes to thecrew operations concept of operations for the use of this switch. TheADT unit 40 also receives an existing ELT activation discrete output 68in parallel to the aircraft avionics systems 28 that receive thisdiscrete. This ELT activation discrete output 68 notifies the ADTinternal monitors and the associated ground segment monitors when an ELThas been activated due to either flight crew activation or internalactivation. A variant of this installation could use only this ELTactivation discrete output 68 and not the flight deck-sourced ELTactivation input 64; data on whether the ELT was activated due to crewor internal inputs would not be available in this case.

For ADTs installed near the ELT, these two inputs could be derived fromthe ELT connector wiring or from wiring close to the installed ELT,resulting in considerable savings in installation time and cost comparedto running new wiring from the flight deck or aircraft avionicsequipment bay. This loosely coupled ADT-ELT configuration providesreduced cost installations due to significantly reduced new wire runrequirements and no new flight deck interface requirements. The re-useof the existing flight deck interface means there is no additional crewtraining or emergency workload from the existing fixed ELT installation,representing an additional reduction of training costs and workloadimpact from the non-integrated ADT-ELT installations.

The monitoring and use of the ELT activation inputs and ELT activationoutput by the ADT allows for synchronization of ADT and ELT distresstransmissions, simplifying and providing for a more coordinated responseby the various receiving ground systems and organizations (airlineoperations centers may be the initial recipients of ADT transmissions;national and international search and rescue organizations may beinitial recipients of the ELT transmissions). This monitoring and use ofthe ELT activation inputs and ELT activation output by the ADT alsoallows for added data on the distress state of the aircraft, i.e., acrew-activated distress state or an ELT G-switch/temperaturesensor-activated distress state.

FIG. 11 shows a tightly coupled (i.e., in series) ADT-ELT integratedarchitecture configuration which, in addition to the benefits describedabove for the non-integrated and loosely coupled configurations (to wit,the ADT use of the existing ELT remote panel interfaces and activationof the ADT distress mode with ELT activation), provides functionalitywith major additional performance benefits. More specifically, thistightly coupled configuration further improves emergency locationperformance by allowing the ADT to trigger ELT distress broadcasts,using, for example, ADT internal trigger conditions indicating aircraftnon-normal or distress flight conditions or ground segment commandsuplinked from an airline operations center. This configuration may alsosupport improved emergency reporting in the presence of SATCOM networkcongestion or RF interference scenarios.

The major difference from the loosely coupled configuration is that theADT unit 40 in the tightly coupled configuration is now placed in seriesbetween the ELT remote panel 22 and the ELT unit 30. Thus the ADT unit40 receives the ELT activation input 64 as shown in FIG. 11. Thisfeature allows the ADT unit 40 to control the activation of the ELT unit30 by sending ADT-ELT activation outputs 72 to the ELT unit 30. Theconventional flight deck activation concept of operations of the ELTunit 30 is still supported by pass-through logic in the ADT unit 40 thatimmediately passes on flight deck commands to the ELT unit 30.Additionally, enhancements to reduce ELT false alarms can be implementedwith ADT filtering of activation commands that are passed on to the ELTunit 30 (for example, by not passing on ELT activation commands when theaircraft is on the ground).

The tightly coupled configuration also allows for significantimprovements to the emergency location performance of the integratedsystems. The ADT aircraft dynamics and state-based trigger functionsthat are used to activate ADT abnormal or distress transmissions canalso be used to activate the fixed ELT upon the detection of abnormalaircraft dynamics or states and prior to a crash.

The addition of ELT triggering by the ADT trigger functions alsoenhances integrated system performance by providing a redundant path(via the ELT COSPAS-SARSAT transmissions) for pre-crash emergencytransmissions in the event that the ADT SATCOM transmissions areunreliable, for example, due to network congestion, gaps in SATCOMconstellation coverage or interference from other on-aircraft systems(for example, Inmarsat to Iridium interference).

Ground segment activation of the existing ELTs over the ADT satelliteconnection is also possible, which may provide advantages for somelocating/tracking scenarios since the ELTs provide local beacontransmissions as well as satellite uplink transmissions.

These added functions address both ADT and ELT shortcomings and providefunctionality similar to (although possibly better than in some areasand not as good in others) to the proposed second-generation ELTs. Thistightly integrated ADT-ELT configuration potentially provides thesebenefits with fewer avionics updates and aircraft installation impactsand hence for less cost and at a potentially earlier time, therebysupporting potentially earlier and larger airline uptake.

FIG. 12 shows an ADT-ELT integrated architecture configuration withmedium coupling (i.e., the ELT unit 30 and ADT unit 40 are in paralleland in series (referred to herein as “enhanced parallel”)) that providesmost of the benefits of the tightly coupled configuration with most ofthe reduced certification risk of the loosely coupled configuration. Akey feature for the ADT-ELT activation output illustrated in FIG. 12 isthat it is coupled into the existing ELT remote panel switch-to-ELT unitcontrol path by an OR circuit (not shown), meaning that either themanually operated switch on the ELT remote panel 22 or the ADT unit 40can activate the ELT unit 30 independently of each other. This allowsthe activation of the ELT unit 30 either in response to flight deck ELTactivation inputs 64 per the existing concept of operations or inresponse to ADT-ELT activation outputs 72 from the ADT unit 40 triggeredby the latter's own trigger determination logic. Using this “OR”connection allows the ADT unit 40 to apply advanced triggeringcapabilities to existing ELTs with no changes to the ELTs and very minorchanges to the existing ELT wiring (and no ELT installation changes).This “OR” configuration reduces the certification risk since theexisting ELT remote panel switch-to-ELT unit control path is maintainedintact.

An ADT interface architecture which addresses several key aspects ofintegrating ADTs and other potential devices with existing fixed ELTinstallations and their associated existing aircraft interfaces will nowbe described with reference to FIGS. 13 and 14. This interfacearchitecture provides the functions that interact with the ELT andaircraft interfaces in the multiple ways required to support the variousintegrated configurations described above and, of equal importance, itdoes so in a manner that is applicable across multiple aircraft modelswith different ELT flight deck controller types and ELTs from a range ofdifferent manufacturers (hence the “common” qualifier for these inputs).The integration of these functions into the existing ADT functionsprovides the benefits described for the non-integrated and looselycoupled ADT-ELT configurations. These functions and their integrationinto the existing ADT functions will now be described in detail.

FIG. 13 identifies inputs to and outputs from an ADT unit 40 that can beincorporated in any one of the configurations depicted in FIGS. 4 and6-12. In some configurations, not all of the inputs to and outputs fromthe ADT unit 40 are used. The ADT unit 40 receives radio frequency (RF)inputs from the ADT antenna 44, including satellite communications(SATCOM) RF inputs 58 (e.g., messages from the ground segment over theIridium network), GPS RF inputs 60 and GLONASS RF inputs 62. The ADTunit 40 interfaces with the ELT flight deck remote panel. This interfaceallows the flight crew to activate the ADT distress transmission rate(i.e., flight crew activation inputs 64, 65). The ADT unit 40 hasprovisions for an output to provide notification to the flight crew ofADT distress transmissions (i.e., ADT distress outputs 66). The ADT unit40 receives input DC power either directly from an aircraft power bus orthrough a battery module. This interface also provides indication ofloss of aircraft power (i.e., aircraft power inputs 76) if the batterymodule is the direct power source. The ADT unit 40 provides SATCOM RFoutputs 74 to the ADT antenna unit 44 (e.g., messages to the groundsegment over the Iridium network). The ADT unit 40 has a maintenanceEthernet interface 78 to support maintenance actions and data loads. TheADT unit 40 has provisions to support detecting the ELT activation input68 from the ELT unit 30 and to provide an ELT activation output 72 tothe ELT unit 30. The ADT unit 40 supports discrete inputs 70 from theaircraft avionics systems 28.

FIG. 14 is a diagram identifying major functions and interfaces of theADT unit 40 which enable the multiple configuration options describedabove. The functions which are inherent to an ADT include the following:an ADT position and attitude data function 102; an ADT ground data linkfunction 104; an ADT trigger logic and aircraft behavior state estimator106; and an ADT position/state reporting function 108.

The ADT position and attitude data function 102 determines the currentaircraft position (including altitude and velocities) and attitude fromexternal (e.g., GNSS) and internal (e.g. internal sensors). Morespecifically, The ADT position and attitude data function 102 takesinput data from GNSS RF inputs, digital airplane navigation inputs, datafrom internal sensors and data validity inputs and estimates andcombines these per internal source prioritization logic or an inputground segment source command to provide high-quality estimates ofaircraft location, speeds, track, attitudes and rates for use by otherADT functions and for aircraft location/state reports.

The ADT ground data link function 104 provides communication to and fromthe associated ground segment via the SATCOM network.

The ADT trigger logic and aircraft behavior state estimator 106integrates aircraft position and attitude data, aircraft state data,ground segment commands and aircraft inputs to determine the ADTestimated aircraft behavior state and associated ADT reportingstate—typically normal, abnormal or distress. More specifically, the ADTunit 40 uses an autonomous aircraft behavior state estimator algorithmto internally generate triggers for alerts and distress calls. Theaircraft behavior estimate is based on the integration of four separate(but related) components or aspects of the observed aircraft state: theon-ground or airborne estimate, abnormal rates or attitudes for a givenlocation as determined by dynamic trigger conditions, unusual altitudesfor a given location and the loss of aircraft power inputs. The ADT unit40 estimates aircraft behavior state using the internal GNSS, internalattitude and rate sensor data or aircraft input navigation data (ifavailable) and aircraft power inputs.

The ADT position/state reporting function 108 reports aircraft positionand state data at rates determined by the ADT trigger logic and aircraftbehavior state estimator 106.

In some cases these inherent ADT functions may have additionalinterfaces added or additional internal logic added or modified tosupport the capabilities needed to enable the various integrated ADT-ELTconfigurations.

A second group of functions depicted in FIG. 14 are the ADT interfacefunctions, including the following: a common aircraft discrete inputinterface 112; a common aircraft discrete output interface 114; a commonELT crew activation input interface 116; a common ELT activation inputinterface 118; and a common ELT activation output interface 120.

The final ADT function shown in FIG. 14 is the ELT activation logic 110.This function together with the common ELT activation output interface120 enable implementation of the tightly and medium coupled ADT-ELTconfigurations. The logic components of this function are described indetail below with reference to FIG. 22.

FIG. 15 is a diagram depicting functions that the common aircraftdiscrete input interface 112 should include to support a broad range ofaircraft avionics integration options. The common aircraft discreteinput interface 112 provides a basic interface for use in integratingthe ADT trigger functions with aircraft state inputs from the aircraftavionics systems 28 that may have different sources and implementationsacross different aircraft models and with different aircraft avionicsarchitectures. The common aircraft discrete input interface 112comprises a group of discrete-type inputs. These could be a single inputbut would typically support multiple separate inputs. Each input wouldbe a typical aircraft discrete input. Each input is a single wire inputwhich, combined with the ADT ground input, would support detecting anopen or grounded state for the discrete input.

Referring to FIG. 15, the common aircraft discrete input interface 112comprises high-impedance buffer circuitry 134 and ADT common aircraftdiscrete input logic 140. The circuitry of the common aircraft discreteinterface 112 in accordance with one implementation may take the formshown in FIG. 20 (to be described in detail below). The common aircraftdiscrete input interface 112 presents a high impedance so that thediscrete inputs effectively draw no current. The open state for theseinputs indicates either that the input is not activated or that theinput is not present or used. The grounded state indicates that theinput is active. These discretes are integrated into the ADT triggerlogic and aircraft behavior state estimator function via a programmableinput-to-aircraft state map. Table 1 shows typical values for afour-input example of an ADT discrete input mapping.

TABLE 1 Aircraft Behavior Discrete Input State Discrete Input IsDiscrete Input Is Discrete input Inactive Active Discrete input 1 NORMALDISTRESS Discrete input 2 NORMAL DISTRESS Discrete input 3 NORMALDISTRESS Discrete input 4 NORMAL DISTRESS

The aircraft behavior discrete input state map is implemented withdefault values (per the typical values shown above) and is updateablevia ADT configuration file updates sent via a physical maintenance portupdate or over the air as a configuration update.

The ADT trigger logic and aircraft behavior state estimator 106 uses theaircraft behavior discrete input setting along with the other inputs(other aircraft state data, ground segment inputs, internal ADT sensorinputs etc.) to determine the estimated aircraft behavior state and anyassociated transmission states.

The common aircraft discrete input interface 112 provides a genericmeans to integrate diverse aircraft state inputs into the ADT triggerlogic and hence into the integrated ADT-ELT functionality. Thisinterface requires that an aircraft discrete and the associated discreteactivation logic be present in the aircraft avionics system. Thesourcing of this discrete and the implementation of the associated logicwill vary based on the aircraft model and the associated avionicsarchitecture.

There is also a significant amount of possible variation in the aircraftstate information that this interface may be used to integrate into theADT logic. One possibility is the engine out status for an aircraft. Inthis case, if no applicable discretes were available, then the aircraftavionics logic would be required to be implemented to drive availableaircraft discrete outputs as inputs to the common aircraft discreteinput interface 112.

This approach limits the by-aircraft model, by-avionics architecture andby-aircraft state input required variability to a single commoninterface. This interface is implemented with a generic, widelyavailable set of physical inputs. The inputs from this interface arepre-integrated to the ADT trigger logic via an updateable, flexiblemapping logic.

One alternative or complementary implementation of this interface couldinclude other forms and polarities of discrete inputs (for example, a5-V level is high/active and 0 V is low/inactive) to support a widervariety of potential discrete sources. Another alternative orcomplementary implementation of this interface could include avionicsdigital busses such as ARINC-429, ARINC-629 or ARINC-664/Ethernet inputsto provide the applicable aircraft state inputs in digital form.

FIG. 16 is a diagram depicting functions that an ADT common aircraftdiscrete output interface 114 should include in order to support a broadrange of aircraft avionics integration options. The switch function iscontrolled by the ADT trigger logic and aircraft behavior stateestimator 106. The common aircraft discrete output interface 114provides a means for annunciating entry into and exit from an aircraftdistress state to connected aircraft avionics systems 28. This interfaceuses a discrete format that follows one commonly used by multiple modelsof ELTs. This output is a single-wire input which, combined with the ADTground input, supports providing an open or grounded state for thediscrete output. The common aircraft discrete output interface 114presents a high impedance so that these inputs effectively draw nocurrent.

The common aircraft discrete output interface 114 would typically not beused in an ADT-ELT configuration unless there is a requirement for crewor system notification of ADT distress state activation. It is morelikely that this interface would be used in an ELT replacementinstallation where it is “plug-and-play” compatible with existing ELT ONinterfaces to the aircraft avionics systems and would be used to supporttest/reset concepts of operations equivalent to the replaced ELT orcrew/system activation notification concepts of operations if required.

The aircraft discrete output state is implemented with typical/defaultvalues as shown in Table 2 and is updateable via ADT configuration fileupdates sent via a physical maintenance port update or over the air as aconfiguration update. This common discrete output approach limits theby-aircraft model, by-avionics architecture and by-aircraft state inputrequired variability for providing single common interface. Thisinterface is implemented with generic, widely available set of physicaloutputs that is compatible with the existing ELT ON outputs that arecurrently integrated with a number of aircraft systems. The outputs fromthis interface are pre-integrated with the ADT trigger logic via aflexible, updateable mapping logic that both supports an ELT likeannunciation concept of operations if needed or other uses if needed.

An alternative or complimentary implementation of this interface couldinclude other forms and polarities of discrete inputs (for example, 5 Vlevel is high/active and 0 V is low/inactive) to support a wider varietyof potential discrete receivers in the aircraft avionics.

TABLE 2 Aircraft Discrete Output State Discrete Input Is Discrete InputIs Inactive (Open) Active (Grounded) ADT NOT DISTRESS DISTRESS ReportingState

Another alternative or complimentary implementation of this interfacecould include avionics digital bus-compatible output such as ARINC-429,ARINC-629 or ARINC-664/Ethernet inputs to provide the inputs to theapplicable aircraft avionics in digital form.

Still referring to FIG. 14, the common ELT crew activation inputinterface 116 is used in all of the previously described coupled ADT-ELTconfigurations. This interface provides the means for the ADT unit 40 todetect the flight deck activation of the ELT unit 30 using existingflight deck controllers (e.g., the ELT remote panel 22). The common ELTcrew activation input interface 116 comprises a pair of switchconfigurations that can be supported by two signal wires and the ADTground. The use of the input signals for these switch configurations isshown in Table 3.

FIGS. 17A and 17B depict the internal wiring of the flight deck panelswitch in accordance with the respective ELT remote panel switchconfigurations listed in Table 3. The left side of these figuresrepresents the functionality in the switches (i.e., external to the ADTunit). When the ELT remote panel switch is set to ARM (EXTERNAL ONsignal is an open circuit), the ADT unit sets the Flight Crew InputState to ARM; when the ELT remote panel switch is set to ON (EXTERNAL ONsignal is a grounded circuit), the ADT unit sets the flight crew inputstate to ON.

TABLE 3 Switch Configuration 1 Switch Configuration 2 Input Signals ELTARM ELT ON ELT ARM ELT ON ELT External Open Grounded Open Shorted to ONELT Common ELT Common n/a n/a Open Shorted to ELT External ON ADT Ground— — n/a n/a

FIG. 17C depicts a common ELT crew activation input interface 116 thatallows ADT integration with either of the switch configurations shown inFIGS. 17A and 17B. The common ELT crew activation input interface 116comprises high-impedance buffer circuitry 134 and common ELT crewactivation input logic 136. The circuitry of the common ELT crewactivation input interface 116 in accordance with one implementation maytake the form shown in FIG. 20 (to be described in detail below). Thecommon ELT crew activation input logic 136 ORs the two switchconfigurations together to determine the ELT ARM or ELT ON states. Thusthe common ELT crew activation input interface 116 does not need to bepre-configured for a particular switch configuration. This input signalstate-to-ELT crew activation state mapping is shown in Table 4, in whichthe “Input Signals” are from either the ELT remote panel 22 or from theADT distress activation control 42 (see FIG. 14), and “ELT ARM” and “ELTON” are the corresponding activation states output by the common ELTcrew activation input interface 116 to the ADT trigger logic andaircraft behavior state estimator 106 (see FIG. 14).

The outputs from the high-impedance buffer circuitry 134 will be thesame as the inputs to this buffer circuitry. This buffer circuitryensures that the interface circuits do not draw significant current fromthe input circuits and are solely sensing the state of those inputs,

TABLE 4 Signals Input to Common ELT Crew States Output by Common ELTActivation Input Crew Activation Input Interface Interface ELT ARM ELTON ELT External ON Open Grounded OR Shorted to Common ELT Common OpenOpen OR Shorted to External ON

(1) For the case where a switch is used that references the ELT ExternalON line to the ELT COMMON He, the input to the buffer circuitry 134 andthe output from the buffer circuitry 134 will be as follows:

(a) If the ELT switch is activated (switch in ON position), then “ELTExternal ON” to “ELT COMMON” impedance=zero (closed circuit) and “ELTExternal ON” to GROUND impedance=infinite (open circuit).

(b) If the ELT switch is not activated (switch in “ARM” position), then“ELT External ON” to “ELT COMMON” impedance=infinite (open circuit) and“ELT External ON” to GROUND impedance=infinite (open circuit).

(2) For the case where a switch is used that references the ELT EXTERNALON line to GROUND, the input to the buffer circuitry 134 and the outputfrom the buffer circuitry 134 will be as follows:

(a) If the ELT switch is activated (switch in ON position), then “ELTExternal ON” to GROUND impedance=zero (closed circuit) and “ELT ExternalON” to “ELT COMMON” impedance=infinite (open circuit).

(b) If the ELT switch is not activated (switch in “ARM” position, then“ELT External ON” to GROUND impedance=infinite (open circuit) and “ELTExternal ON” to “ELT COMMON” impedance=infinite (open circuit).

The common ELT crew activation input logic 136 operates such that if itsees either “ELT External ON” to GROUND impedance=zero (closed circuit)OR “ELT External ON” to “ELT COMMON” impedance=zero (closed circuit) itconsiders the ON command to be active.

This activation portion of the interface thus detects the two primaryELT crew activation states of ARM (the ELT is not active but is ready totransmit upon internal or external activation input) and ON (the ELT hasbeen activated and is broadcasting distress signals). Test/reset signalsare not detected by this interface directly, but would be seen as atransient ON signal on the activation portion of the interface and canbe inferred by the ADT. The mapping of the activation states output bythe common ELT crew activation input interface 116 to the aircraftstates estimated by the ADT trigger logic and aircraft behavior stateestimator 106 (see FIG. 14) is shown in Table 5.

TABLE 5 States Output by Aircraft States Estimated Common ELT Crew byADT Trigger Logic and Activation Input Aircraft Behavior State InterfaceEstimator ELT ARM NORMAL ELT ON DISTRESS ELT ON Transient ABNORMAL/TEST(ELT TEST)

The ELT crew activation input state map is implemented with defaultvalues and is updateable via ADT configuration file updates sent via aphysical maintenance port update or over the air as a configurationupdate.

To summarize the foregoing, the switch position is set by the crew usingthe ELT remote panel 22 or the ADT distress activation control 42(depending on what is installed). The open/grounded configuration set bythe switch position and the switch type are interpreted by the commonELT crew activation input interface 116 as either “ELT ARM” or “ELT ON”,as described in Table 4. Then the output from the common ELT crewactivation input interface 116, i.e., “ELT ARM”, “ELT ON” or a transient“ELT ON”, are mapped to various aircraft state estimates (“Normal”,“Distress” or “Abnormal/Test”) per Table 5 in the ADT trigger logic andaircraft behavior state estimator 106. The aircraft state estimates fromthese crew inputs are then combined with other aircraft state estimatesin the ADT trigger logic and aircraft behavior state estimator 106. Thisother logic and the fusion logic are disclosed in U.S. patentapplication Ser. No. 14/858,235, the disclosure of which is incorporatedby reference herein in its entirety.

This common ELT crew activation input approach allows the re-use of theexisting ELT flight deck switch types and switches themselves (and muchof the associated wiring) that is a key enabler for reduced costs. Thisapproach also allows for improved synchronization of the ADT-ELTresponses for the loosely coupled ADT-ELT configuration and is a keycomponent of putting the ADT in the ELT control path for the tightlycoupled ADT-ELT configuration. The reduction of the high by-aircraft andby-ELT switch complexity to a fairly simple common ADT interface is asignificant enabler for this approach. The choice to only use the ELTactivation portion of the interface reduces complexity and associatedtechnical and certification risks.

The common ELT crew activation input interface 116 can be pre-integratedwith the ADT trigger logic and aircraft behavior state estimator 106 viaa flexible, updateable mapping logic that supports the use of the fightdeck ELT activation switch as a high priority indication of aircraftdistress state in the default configuration or supporting otherprioritizations via changes in the mapping if required.

The common ELT activation input interface 118 detects ELT activationusing an existing ELT ON discrete output (i.e., ELT activation output68) that is common across a range of existing ELTs. This discrete outputis used by the ELT unit 30 to signal the aircraft avionics systems 28that the ELT unit 30 has been activated, either due to crew inputs ordue to internal ELT sensors (e.g., a G-switch set off by a highde-acceleration).

The common ELT activation input interface 118 is implemented as a singlewire plus the ADT ground physical input. As seen in FIG. 18, the commonELT activation input interface 118 comprises high-impedance buffercircuitry 134 and common ELT discrete activation input logic 138. Thecircuitry of the common ELT activation input interface 118 in accordancewith one implementation may take the form shown in FIG. 20 (to bedescribed in detail below). The common ELT discrete activation inputlogic 138 determines the ELT state as a function of the discrete input.The signal values-to-ELT state mapping for common ELT activation inputinterface 118 is shown in Table 6.

TABLE 6 Discrete States of Common ELT States of ELT unit ActivationInput Interface ELT ARM or not Discrete Input Is Inactive (Open)connected ELT ON Discrete Input Is Active (Grounded)

This mapping is updateable via ADT configuration file updates sent via aphysical maintenance port update or over the air as a configurationupdate if there is a requirement to tailor the inputs for a differentconfiguration, but this default mapping covers a wide range of ELTconfigurations.

The common ELT activation input interface 118 provides redundant andcomplementary data to the common ELT crew activation inputs. The mappingof the common ELT activation input builds on the state of the common ELTcrew activation input as shown in Table 7. The mapping shown in Table 7is implemented with default values and is updateable via ADTconfiguration file updates sent via a physical maintenance port updateor over the air as a configuration update.

TABLE 7 States Aircraft States States Output Output by Estimated by byCommon Common ELT ADT Trigger ELT Crew Activation Logic and Notes(Specific Activation Input Aircraft Behavior Crew/ELT Input InterfaceInterface state estimator Activation State) ELT ARM ELT ARM NORMALNon-Activated ELT ELT ON ELT ON DISTRESS Crew Activation of ELT ELT ONELT ARM or DISTRESS Crew Activation Not Connected of ELT ELT ARM ELT ONABNORMAL ELT Self- Activation ELT ON ELT ON ABNORMAL/ Test ActivationTransient Transient TEST of ELT (ELT TEST) (ELT TEST)

The common ELT crew activation input interface 116 allows the ADT unit40 to detect crew activation of the ELT unit 30. The common ELTactivation input interface 118 provides a redundant path for thatdetection and adds visibility for non-crew-initiated ELT activations.This added visibility improves situational awareness at airlineoperations centers by adding the source of the ELT activation to the ADTreporting and supports improved synchronization between airlineoperations centers and rescue centers due to a common ELT activationsituational picture.

The common ELT activation input interface 118 is pre-integrated with theADT trigger logic via a flexible, updateable mapping logic that supportsthe use of the basic ELT concept of operations to provide additionalinformation to an airline operations center in the default configurationor supports other prioritizations via changes in the mapping ifrequired.

The common ELT activation output interface 120 is a component used inthe tightly coupled (i.e., series) and medium coupled (i.e., enhancedparallel) ADT-ELT configurations shown in FIGS. 11 and 12. Thisinterface provides the means for the ADT unit 40 to control theactivation of the ELT unit 30 using existing ELT control inputs. Thisinterface uses the same approach (building on the same data) asdescribed with reference to the common ELT crew activation inputinterface 116 to provide ELT activation outputs applicable for a widerange of ELT types and aircraft installation configurations.

The common ELT activation output interface 120 provides two signaloutputs (and the associated ADT ground) that support the two switchconfigurations previously identified as providing a broadly applicableELT activation interface. These output signals are high-impedanceOpen/Grounded discrete signals that provide the functionality of the twoswitch configurations shown in FIGS. 19A and 19B. The output signals areconfigured as shown in Table 8 based on the command from the ELTactivation logic 110 (see FIG. 14) for the ELT ARM or ELT ON state.

TABLE 8 ADT Output Switch Configuration 1 Switch Configuration 2 SignalsELT ARM ELT ON ELT ARM ELT ON ELT External Open Grounded Open Shorted toON Common ELT Common n/a n/a Open Shorted to External ON ADT Ground — —n/a n/a

For a given ELT type/installation configuration, the associated switchconfigurations shown in FIGS. 19A and 19B respectively can be inferredfrom the signal configurations seen on the common ELT crew activationinput or would be entered as a configuration data entry (updateable overthe air or via the maintenance port). Both switch configurations shownin FIGS. 19A and 19B use the ELT External ON Signal. If the ELT Commonsignal is not used for a given configuration, then this would not haveto be connected. As seen in FIG. 19C, the common ELT activation outputinterface 120 comprises a configuration that emulates both of the remoteswitch configurations depicted in FIGS. 19A and 19B. The switch functionis controlled by the ELT activation logic 110.

More specifically, the ADT unit pass-through function uses the outputconfiguration that is equivalent to the received crew activation inputs.The ADT unit sets the pass-through function outputs to ARM by settingthe ELT EXTERNAL ON signal to an open circuit with respect to ground andwith respect to the ELT COMMON signal. The ADT unit sets thepass-through function output to ON by setting the ELT EXTERNAL ON signalto a closed circuit with respect to ground or with respect to the ELTCOMMON signal following on the crew activation input configuration. Whenthe ELT control panel switch is set to ARM, the ADT unit sets thepass-through function outputs to ARM within a short period of time(e.g., 0.1 second). When the ELT control panel switch is set to ON, theADT unit sets the pass-through function outputs to ON within the sameshort period of time.

The common ELT activation output state map is implemented with defaultvalues and is updateable via ADT configuration file updates sent via aphysical maintenance port update or over the air as a configurationupdate.

FIG. 20 shows electronic circuitry incorporated in the ADT unit andconfigured to perform the interfacing and other functions disclosedherein in accordance with some embodiments. This electronic circuitryincludes the high-impedance buffer circuitry 134, an analog-to-digitalconverter 154 (e.g., a discrete-to-digital converter), a microcontroller156, and a microprocessor 158, connected in series. The microprocessor158 can be programmed to execute one or more of the interface sensorfunctions identified in FIGS. 17C, 18 and 19C. The electronic circuitrydepicted in FIG. 20 may be common to the common aircraft discrete inputinterface 112, the common ELT crew activation input interface 116, andthe common ELT activation input interface 118. In the alternative, theindividual interfaces may incorporate the electronic circuitry depictedin FIG. 20.

Optionally, the buffer circuitry 134 may be incorporated in theanalog-to-digital converter 154. The analog-to-digital converter 154 maybe a separate integrated circuit or a built-in discrete input on themicrocontroller 156. The analog-to-digital converter 154 converts theanalog discrete inputs into digital inputs to the microcontroller 156.The microcontroller 156 aggregates various inputs and puts them on adigital bus for input to the microprocessor 158, where the logic wouldbe implemented as a software function. Optionally, the microcontrollerfunctionality may be in the microprocessor 158. Other softwarefunctions, such as the ELT activation logic 110 and the ADT triggerlogic and aircraft behavior estimator 106, may be on the samemicroprocessor hardware platform as the above-described sensor functions136, 138 and 140.

Furthermore, the common aircraft discrete output interface 114 and thecommon ELT activation output interface 120 may each comprise a variationof the electronic circuitry depicted in FIG. 20. The electroniccircuitry in this case would include the same microcontroller 156 andmicroprocessor 158, but instead of an analog-to-digital converter 154between the microcontroller 156 and the high-impedance buffer circuitry134, the electronic circuitry would include any one of the followingintegrated circuits: a digital-to-analog converter, adigital-to-discrete converter, discrete switching or a discrete driveroutput. The microprocessor 158 would feed the microcontroller 156 tocontrol the output discrete states via the common driver/out integratedcircuit.

There are two major alternative smart switch-based embodiments for thediscrete interface architecture shown in FIG. 20.

The first alternative smart switch-based embodiment for the functions inFIG. 20 is to use dedicated discrete-to-digital integrated circuits incombination with either input switching or dedicated input ports andwiring to bring inputs from different discrete types into theappropriate discrete-to-digital circuit interface in place of functions134 and 154. This discrete-to-digital interface integrated circuit couldbe interconnected directly with the microprocessor 158 hosting theassociated software function or to the microprocessor via amicrocontroller 156 providing digital data combination, translation andqueuing-to-a-digital-bus functions.

The second alternative smart switch-based embodiment would be to use theanalog-to-digital converter 154 with its broad capabilities to sense andinterpret the input signal values. This analog-to-digital converter 154would be interconnected directly with an microprocessor 158 hosting theassociated software function or to the microprocessor 158 via amicrocontroller 156 providing digital data combination, translation andqueuing-to-a-digital-bus functions. In this case an additional functionin software hosted in the microprocessor or as firmware in an interfacecircuit (for example, a field programmable gate array or a programmablelogic device) would be added that would determine the discrete typeconnected and interpret the inputs received for the logic functions inthe microprocessor software.

Both alternatives could lead to single part number device that couldwork across a very broad and disparate fleet of airplane configurations.A smart switch-based architecture could also be leveraged to detecttampering or system failures.

FIG. 21 is a diagram identifying components of the ADT trigger logic andaircraft behavior state estimator 106 in accordance with one embodimentof the ADT unit 40. The ADT processor 88 (see FIG. 5) uses an autonomousalgorithm, referred to herein as the aircraft behavior state estimator106 a, to internally generate triggers for alerts and distress calls.This is the logic that allows early detection of an aircraft in distressand hence the early triggering and longer duration broadcasts thatprovide improved emergency detection benefits. The aircraft behaviorstate estimator 106 a comprises an aircraft-on-ground estimator 142 andaircraft behavior dynamic trigger state functionality 144, both of whichreceive aircraft navigation inputs from the ADT position and attitudedata function 102 (see FIG. 14). The ADT unit has internal sensors todetermine aircraft position, trajectory and attitude information inconjunction with GNSS or input aircraft navigation data The aircraftbehavior state estimator 106 a depicted in FIG. 21 further comprisesaircraft behavior input discrete state functionality 146, which receivesaircraft discrete inputs from the aircraft avionics system 28 by way ofthe common aircraft discrete input interface 112 (see FIG. 14).

FIG. 21 shows the logic flow for the aircraft behavior state estimator106 a. The aircraft behavior estimate is based on the integration ofseveral components or aspects of the observed aircraft state: theon-ground or airborne estimate, abnormal rates or attitudes for a givenlocation as determined by dynamic trigger conditions, and the state ofaircraft discrete inputs from the aircraft avionics systems. Theon-ground or airborne state of the aircraft is estimated by theaircraft-on-ground estimator 142; the abnormal rates or attitudes aredetermined by the aircraft behavior dynamic trigger state functionality144; and the state of aircraft discrete inputs is determined by theaircraft behavior input discrete state functionality 146. The resultsare input to the aircraft behavior state setting logic functionality148, which outputs signals indicating the estimated state of theaircraft. The possible states include: normal, abnormal and distress (orpre-crash) behavior. The aircraft behavior state estimator 106 a alsooutputs whether the aircraft is airborne or on-the-ground (landed).

The aircraft-on-ground estimator 142 uses aircraft speed and altitude toestimate whether the aircraft is on the ground (e.g., landed) or in theair. The aircraft behavior state setting logic 148 is configured tosuppress the dynamic trigger conditions (from aircraft behavior dynamictrigger state functionality 144) and aircraft discrete inputs (fromaircraft behavior input discrete state functionality 146) for settingaircraft behavior estimate abnormal or distress states if the outputfrom aircraft-on-ground estimator 142 indicates that the aircraft is onthe ground. The aircraft behavior state setting logic 148 is alsoconfigured to output a signal indicating that the estimated aircraftbehavior state is abnormal or distress depending on the state ofaircraft discrete inputs output by the aircraft behavior input discretestate functionality 146. The aircraft behavior state setting logic 148is further configured to output a signal indicating that the estimatedaircraft behavior state is abnormal or distress depending on whether theaircraft behavior dynamic trigger state functionality 144 has detectedan abnormal attitude, speed or altitude.

The aircraft behavior dynamic trigger state functionality 144 uses logicthat compares sensor data to trigger conditions that may indicate anabnormal or distress state, such as unusual attitude (e.g., excessivebank or pitch), unusual speed (e.g., horizontal speed outside a range orexcessive vertical speed), an unusual altitude (e.g., an altitudeoutside of an expected range, and an unusual maneuver (e.g., anexcessive track change). Tables setting forth trigger conditions inaccordance with one configuration can be found in FIGS. 11 through 15 inU.S. patent application Ser. No. 14/858,235, the disclosure of which isincorporated by reference herein in its entirety. Other tables to setnormal, abnormal or distress state conditions while the aircraft is inan airborne state can be used. Geofences, or geographic boundaries, maybe defined to define oceanic or remote versus continental or non-remoteairspace where greater radar and surveillance coverage will be availableto help locate an aircraft in distress. For example, the geofences mayprovide different minimum and maximum altitude thresholds for oceanic oren route flight phases and for flight phases occurring closer to theorigination and destination locations.

The aircraft behavior state setting logic 148 has state settings ofNORMAL, ABNORMAL and DISTRESS. The logic for setting these states is asfollows:

(a) The ADT unit sets the aircraft behavior state to NORMAL when theaircraft is on the ground.

(b) When the aircraft is airborne, the ADT unit sets the aircraftbehavior state to the highest values specified by:

(1) an aircraft behavior dynamic trigger state setting determined by theaircraft behavior dynamic trigger state logic 144 (the aircraft behaviorstate is set to the highest values specified by trigger condition logicof the types indicated in FIGS. 11-15 of U.S. patent application Ser.No. 14/858,235);

(2) a minimum/maximum safe altitude state setting as determined bymaximum/minimum safe altitude logic;

(3) an aircraft behavior power state setting as determined by aircraftbehavior power state transitions logic;

(4) an aircraft behavior ELT state setting as determined by aircraftbehavior ELT state transitions logic;

(5) an aircraft discrete input state setting as determined by aircraftbehavior discrete input state transitions logic; and.

(6) treat any BEHAVIOR INDETERMINATE setting inputs as ABNORMAL statesettings and report the presence of BEHAVIOR INDETERMINATE settings.

The ADT unit uses the following reporting rate hierarchy for determiningthe relative values of the requested Airborne Behavior State:DISTRESS>ABNORMAL>NORMAL (i.e., DISTRESS is the highest aircraftbehavior state, NORMAL is the lowest.)

Still referring to FIG. 21, the aircraft behavior state estimator 106 aoutputs its estimate of the aircraft behavior state (normal, abnormal ordistress) to the ADT trigger logic 106 b. The ADT trigger logic 106 bcomprises ADT trigger logic 150 and ELT activation request logic 152.The ADT trigger logic 150 first determines the transmit state (whetherthe ADT unit is allowed to transmit or not) currently active. Then, ifthe Transmit-ON state is active (i.e., transmissions are allowed), theADT trigger logic 150 determines the appropriate position/state reporttransmit rate based on a worst case input. The ADT trigger logic 150determines the current transmit state (Transmit ON or Transmit OFF)using flight crew activation inputs received from the common ELT crewactivation input interface 116 (see FIG. 14), ground segment commandinputs received from the ADT ground data link function 104 (see FIG.14), and ELT activation inputs received from the common ELT activationinput interface 118 (see FIG. 14). Based on these inputs, the ADTtrigger logic 150 outputs the position/state reporting rate to the ADTposition/state reporting function 108 (see FIG. 14).

Referring again to FIG. 21, the ADT trigger logic 150 also outputs theaircraft behavior state to the ELT activation request logic 152, whichis configured to trigger the ELT unit based on a settable ADT reportingstate (Abnormal or Distress or None). The ELT activation request logic152 outputs the ELT activation request to the ELT activation logic 110(see FIG. 14). The ELT activation request logic 152 also outputs adiscrete indicating ELT activation to the common aircraft discreteoutput interface 114 (see FIG. 14).

If the ADT trigger logic and aircraft behavior state estimator 106detects a distress condition, then an ELT activation signal is sent tothe ELT activation logic 110 and an aircraft discrete output is sent tothe aircraft avionics systems 28 by way of the common aircraft discreteinput interface 114 (see FIG. 14). If the ADT trigger logic and aircraftbehavior state estimator 106 detects an abnormal condition, then an ELTactivation signal may be sent to the ELT activation logic 110 dependingon whether abnormal states are configured to activate the ELT. Analternate implementation is to require the abnormal condition to beactive for a longer time before the ELT is activated. This abnormalstate estimate provides estimates that are not as indicative of a truedistress condition but are indicative of abnormal conditions. Theseabnormal conditions may result in more false positive ELT activations,but may also result in earlier activations in the case of an aircraft indistress. Thus it is envisioned as a configurable state that can beupdated based on operational experience.

For the tightly coupled (see FIG. 11) and medium coupled (see FIG. 12)ADT-ELT configurations, the ELT activation logic 110 provides thecritical bridge between the incoming ELT crew activation inputs, the ADTtrigger logic and aircraft behavior state estimator 106 and the outputELT activation signals that provide the external activation commands tothe ELTs. The basic components of the ELT activation logic 110 are shownin FIG. 22.

At the top level the ELT activation logic 110 may comprise two separatesoftware modules: crew activation inputs logic 122 and trigger inputslogic 128, respectively corresponding to the two potential sources ofELT activation inputs: the flight crew activation inputs coming in viathe common ELT crew activation input interface 116 and the ADTactivation inputs coming in via the ADT trigger logic and aircraftbehavior state estimator 106 (which inputs include aircraft discreteinputs from the avionics system 28 and ground segment-uplinkedactivation commands received via SATCOM).

The crew activation inputs logic 122 in turn comprises two components(e.g., computer routines for executing respective algorithms): crewactivation input pass-through logic 124 and crew activation filteringlogic 126. The basic crew activation input pass-through logic 124 isdesigned to apply the current crew activation input state (e.g., ELT ONor ELT ARM) to the common ELT activation output interface 120 within ashort period of time (on the order of 0.1 second), subject to the crewactivation filtering logic 126. The basic crew activation filteringlogic 126 is designed to allow all crew activations to pass through tothe common ELT activation output interface 120 while the aircraft isairborne and while there is no countermanding ground segment command.Other flight crew activation filters can be applied and this function isimplemented with default values and is updateable via ADT configurationfile updates sent via a physical maintenance port update or over the airas a configuration update.

Similarly, the trigger inputs logic 128 in turn comprises two components(e.g., computer routines for executing respective algorithms): thetrigger activation input pass-through logic 130 and the triggeractivation filtering logic 132. The basic trigger activation inputpass-through logic 130 is designed to apply any aircraft behavior stateof distress as an ELT ON state and any other states as maintaining ELTARM to the common ELT activation output interface 120 within a shortperiod of time (on the order of 0.1 second), subject to the triggeractivation filtering logic 132. The basic trigger activation filteringlogic 132 is designed to allow all ELT activations to pass through tothe common ELT activation output interface 120 while the aircraft isairborne and while there is no countermanding ground segment command.Other trigger activation filters can be applied and this function isimplemented with default values and is updateable via ADT configurationfile updates sent via a physical maintenance port update or over the airas a configuration update.

For conflicting or differing flight crew and trigger input values, thehighest priority goes to the input with the greatest severity level,i.e., an input of ELT ON supersedes an input of ELT ARM.

While apparatus and methods have been described with reference tovarious embodiments, it will be understood by those skilled in the artthat various changes may be made and equivalents may be substituted forelements thereof without departing from the teachings herein. Inaddition, many modifications may be made to adapt the concepts andreductions to practice disclosed herein to a particular situation.Accordingly, it is intended that the subject matter covered by theclaims not be limited to the disclosed embodiments.

The structure corresponding to the “processing means” recited in theclaims comprises one or more processors (e.g., microprocessors) andsoftware modules comprising logic executable by the processor(s). Oneprocessor (or each of two or more processors) may execute logic frommore than one software module. Alternatively, the respective logic of amultiplicity of software modules can be executed by a respectivemultiplicity of processors. In claims that recite “first processingmeans” and “second processing means”, the respective correspondingstructures for performing the processing function include at least thefollowing configurations: (1) first and second software modules (of thefirst and second processing means respectively) which have their logicexecuted by the same processor; and (2) first and second softwaremodules which have their logic executed by first and second processorsrespectively.

The process claims set forth hereinafter should not be construed torequire that the steps recited therein be performed in alphabeticalorder (any alphabetical ordering in the claims is used solely for thepurpose of referencing previously recited steps) or in the order inwhich they are recited. Nor should they be construed to exclude anyportions of two or more steps being performed concurrently oralternatingly.

The invention claimed is:
 1. An ADT unit comprising: first processingmeans comprising ELT activation logic; and an input interface comprisingfirst, second and third terminals and second processing means configuredto output an ELT ON state signal to the ELT activation logic if animpedance between the first and third terminals is effectively zero orif an impedance between the first and second terminals is effectivelyzero.
 2. The ADT unit as recited in claim 1, wherein the first andsecond processing means comprise a common processor.
 3. The ADT unit asrecited in claim 1, wherein the first processing means comprise a firstprocessor and the second processing means comprises a second processor.4. The ADT unit as recited in claim 1, wherein the input interfacefurther comprises a high-impedance buffer circuit connected to thefirst, second and third terminals.
 5. The ADT unit as recited in claim4, wherein the input interface further comprises an analog-to-digitalconverter between the high-impedance buffer circuit and the secondprocessing means.
 6. The ADT unit as recited in claim 1, wherein thefirst processing means further comprises an aircraft behavior stateestimator and ADT trigger logic that receives an estimated aircraftbehavior state signal from the aircraft behavior state estimator and theELT ON state signal from the second processing means, and is configuredto send an ELT activation request signal to the ELT activation logic ifthe estimated aircraft behavior state signal indicates an abnormal ordistress state or an ELT ON state signal has been received.
 7. A systemonboard an aircraft comprising: an ELT remote panel on the flight deckof the aircraft, the ELT remote panel comprising a switch; a firstantenna that is attached to an exterior of a fuselage skin of theaircraft; and an ADT unit connected to the first antenna and comprising:first processing means comprising ELT activation logic; and a firstinput interface comprising first, second and third terminals, and secondprocessing means configured to output an ELT ON state signal to the ELTactivation logic if an impedance between the first and third terminalsis effectively zero or if an impedance between the first and secondterminals is effectively zero, wherein the switch of the ELT remotepanel is connected to the first terminal of the first input interface bywiring.
 8. The system as recited in claim 7, wherein the first andsecond processing means comprise a common processor.
 9. The system asrecited in claim 7, wherein the first processing means comprise a firstprocessor and the second processing means comprises a second processor.10. The system as recited in claim 7, wherein the switch of the ELTremote panel is not connected to either of the second and thirdterminals of the first input interface and the third terminal of thefirst input interface is connected to ground.
 11. The system as recitedin claim 7, wherein the switch of the ELT remote panel is also connectedto the second terminal of the first input interface by wiring.
 12. Thesystem as recited in claim 7, wherein the first input interface of theADT unit further comprises: a high-impedance buffer circuit connected tothe first, second and third terminals; and an analog-to-digitalconverter between the high-impedance buffer circuit and the secondprocessing means.
 13. The system as recited in claim 7, furthercomprising: a second antenna that is attached to an exterior of afuselage skin of the aircraft; and an ELT unit connected to the secondantenna and to the ADT unit.
 14. The system as recited in claim 13,wherein the ELT unit is also connected to the switch of the ELT remotepanel.
 15. The system as recited in claim 13, wherein the ADT unitfurther comprises a first output interface that comprises a terminalconnected to the ELT unit and third processing means configured tooutput an ELT ON state signal to the terminal of the first outputinterface in response to receipt of an ELT ON state signal from the ELTactivation logic.
 16. The system as recited in claim 15, wherein the ELTactivation logic comprises trigger activation filtering logic andtrigger activation input pass-through logic configured to apply the ELTON state signal to the terminal of the first output interface subject tothe trigger activation filtering logic.
 17. The system as recited inclaim 13, wherein the first processing means further comprises anaircraft behavior state estimator and trigger logic that receives anestimated aircraft behavior state signal from the aircraft behaviorstate estimator and the ELT ON state signal from the second processingmeans, the trigger logic being configured to send an ELT activationrequest signal to the ELT activation logic if the estimated aircraftbehavior state signal indicates an abnormal or distress state or an ELTON state signal has been received.
 18. The system as recited in claim17, wherein the ELT activation logic comprises crew activation filteringlogic and crew activation input pass-through logic configured to applythe ELT ON state signal from the second processing means to the terminalof the first output interface subject to the crew activation filteringlogic.
 19. The system as recited in claim 13, further comprising anaircraft avionics system, wherein the ADT unit further comprises asecond input interface and a second output interface connected to theaircraft avionics system by wiring.